<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box {
       width: 100px;
       height: 100px;
       background-color: rgb(247, 0, 255);
   }
   </style>
</head>
<body>
    <div class="box">
        <!-- 元素无厚度 -->
        <div class="inner">inner</div>
    </div>
</body>
</html>